As an apparatus for polishing a surface of a semiconductor wafer such as a silicon wafer, there are a single-side polishing apparatus, in which the workpiece is polished by each side, and a double-side polishing apparatus, in which the both sides of the workpiece are polished at the same time.
For example as shown in FIG. 10, a common single-side polishing apparatus comprises a turn table 73 onto which a polishing pad 74 is attached, a polishing agent supply mechanism 76, a polishing head 72 and the like. The polishing apparatus 71 polishes a wafer W by holding the wafer W with the polishing head 72, supplying the polishing agent 75 to the polishing pad 74 through the polishing agent supply mechanism 76, rotating the turn table 73 and the polishing head 72 respectively, and bringing the surface of the wafer W into sliding contact with the polishing pad 74.
As a method for holding the workpiece, there are a method of sticking the workpiece on a flat disklike plate with an adhesive such as wax, a method of sticking with water the workpiece on a soft pad (a backing pad), a method of sucking the workpiece with vacuum, or the like.
FIG. 11 illustrates a schematic example of a polishing head holding the workpiece with the backing pad. This polishing head 91 has the backing pad 95 that is made of polyurethane and the like and is attached on the lower face of a disklike carrier 92 made of ceramic or the like. The pad 95 is caused to absorb with water to hold the workpiece W with surface tension. In addition, in order to prevent the workpiece W from coming off from the carrier 92 during the polishing, a ring-shaped template 94 is provided around the carrier 92.
In the case of polishing a large diameter workpiece, such as a silicon single crystal wafer particularly having a diameter of 300 mm, using a plane polishing pad without a groove, there is a problem such that when the polishing head is lifted to attempt to demount the workpiece from the polishing pad after polishing the workpiece, the polished workpiece adheres to a surface of the polishing pad due to surface tension of the polishing agent and thereby the workpiece remains on the polishing pad. In addition, there is a problem such that when suction power of the polishing head for the workpiece excessively increases, such a load that lifts the turn table is added to bearing parts that fix the turn table.
In view of the problems, for example, a method is adopted in which the suction power of the polishing pad is reduced by forming a groove on the polishing pad or in which the polishing head is lifted after the polishing head is overhung from the turn table once (hereinafter referred to as an overhang method. For example, see Japanese Patent Application Laid-open (kokai) No. 2001-341070).
However, in the case of forming the groove on the polishing pad, there are quality problems such that minute waviness occurs on the surface of the workpiece due to transfer of the groove of the polishing pad, an edge of the workpiece is caught in the groove part to be damaged, an outer peripheral sag occurs or the like. Besides, in the overhang method there are problems that a size of the apparatus becomes large to keep a space for overhanging the polishing head and the like.